Linux and UNIX Man Pages

embedded_su - allow an application to prompt for credentials and execute commands as the super user or another user

SYNOPSIS

/usr/lib/embedded_su [-] [username [arg...]]

DESCRIPTION

The embedded_su command allows an application to prompt the user for security credentials and then use those credentials to execute a pro-
gram as another user or role (see rbac(5) for information on role-based access control). The default username is root (super user).
embedded_su is identical to su(1M), except that the user interaction is packaged in a form suitable for another program to interpret and
display. Typically, embedded_su would be used to allow a graphical program to prompt for the super user password and execute a command as
the super user, without requiring that the requesting program be run as the super user.
PROTOCOL
embedded_su implements a simple protocol over standard input, standard output, and standard error. This protocol consists of three phases,
roughly corresponding to PAM initialization, the PAM dialog, and PAM completion.
Phase 1: Initialization
After starting embedded_su, the application must send an initialization block on embedded_su's standard input. This block is a text block,
as described under "Text Blocks". There are currently no initialization parameters defined; the application should send an empty block by
sending a line consisting solely of a period (.).
Phase 2: Conversation
embedded_su then emits zero or more conversation blocks on its standard output. Each conversation block may require zero or more responses.
A conversation block starts with a line consisting of the word CONV, followed by whitespace, followed by the number of messages in the con-
versation block as a decimal integer. The number of messages may be followed by whitespace and additional data. This data, if present, must
be ignored.
Each message consists of a line containing a header followed by a text block, as described under "Text Blocks". A single newline is
appended to each message, allowing the message to end with a line that does not end with a newline.
A message header line consists of a PAM message style name, as described in pam_start(3PAM). The message header values are:
PAM_PROMPT_ECHO_OFF The application is to prompt the user for a value, with echoing disabled.
PAM_PROMPT_ECHO_ON The application is to prompt the user for a value, with echoing enabled.
PAM_ERROR_MSG The application is to display the message in a form appropriate for displaying an error.
PAM_TEXT_INFO The application is to display the message in a form appropriate for general information.
The PAM message style may be followed by whitespace and additional data. This data, if present, must be ignored.
After writing all of the messages in the conversation block, if any of them were PAM_PROMPT_ECHO_OFF or PAM_PROMPT_ECHO_ON, embedded_su
waits for the response values. It expects the response values one per line, in the order the messages were given.
Phase 3: Completion
After zero or more conversation blocks, embedded_su emits a result block instead of a conversation block.
Upon success, embedded_su emits a single line containing the word "SUCCESS". The word SUCCESS may be followed by whitespace and additional
data. This data, if present, must be ignored.
Upon failure, embedded_su emits a single line containing the word "ERROR", followed by a text block as described under "Text Bocks". The
text block gives an error message. The word ERROR may be followed by whitespace and additional data. This data, if present, must be
ignored.
Text Blocks
Initialization blocks, message blocks, and error blocks are all text blocks. These are blocks of text that are terminated by a line con-
taining a single period (.). Lines in the block that begin with a "." have an extra "." prepended to them.
Internationalization
All messages are localized to the current locale; no further localization is required.
SECURITY
embedded_su uses pam(3PAM) for authentication, account management, and session management. Its primary function is to export the PAM con-
versation mechanism to an unprivileged program. Like su(1M), the PAM configuration policy can be used to control embedded_su. The PAM ser-
vice name used is "embedded_su".
embedded_su is almost exactly equivalent to su(1M) for security purposes. The only exception is that it is slightly easier to use embed-
ded_su in writing a malicious program that might trick a user into providing secret data. For those sites needing maximum security, poten-
tially at the expense of application functionality, the EXAMPLES section shows how to disable embedded_su.